In conventional drop-on-demand inkjet printing systems, inkjet printheads eject fluid droplets (e.g., ink) through a plurality of nozzles toward a print medium, such as a sheet of paper, to print an image onto the print medium. The nozzles are generally arranged in one or more arrays, such that properly sequenced ejection of ink from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium move relative to one other.
In thermal bubble-type inkjet printing systems, a resistor heating element actuator in an ink-filled chamber vaporizes ink, creating a rapidly expanding bubble that forces an ink droplet out of a nozzle. Electrical current passing through the heating element generates the heat, vaporizing a small portion of the fluid within the chamber. As the heating element cools the vapor bubble collapses, drawing more fluid from a reservoir into the chamber in preparation for ejecting another drop through the nozzle.
Unfortunately, while the hot firing surface of the heating element drives droplet generation, it can also cause related problems in the thermal inkjet (TIJ) printing system. One such problem is the phenomenon known as ‘kogation’, which is the buildup of residue (koga) on the firing surface of the heating element. The repeated heating of the element and ink can cause a breakdown of pigments and other ink components, resulting in the fouling of the heating element surface. The buildup of koga on the firing surface of the heating element acts as an insulating barrier which reduces the efficiency of the vaporization process at the firing surface. The result is a reduction in volume and velocity of the ink droplet ejected from the printhead nozzle, and a corresponding decrease in print quality that can be seen on the print medium.